1. Technical Field
This application relates to methods and systems for performing radio occultation (RO) for inferring physical properties of a portion of atmosphere, e.g., of a portion of Earth's atmosphere, by receiving signals from Global Navigation Satellite System (GNSS) satellites.
2. Description of the Related Art
Radio occultation using GPS signals was proposed by the Jet Propulsion Laboratory (JPL) in 1988, based on experience gained from several planetary missions. The first radio occultation experiment was carried out by the GPS Meteorological mission (GPS/MET), launched in 1995. Other missions followed GPS/MET, such as the Challenging Mini-satellite Payload (CHAMP) and the Satellite de Aplicaciones Cientificas-C (SAC-C) in 2000, and the Gravity Recovery and Climate Experiment (GRACE-A) in 2002, to name the very early ones.
Currently there is a number of space-borne missions, even full constellations, carrying (or planned to carry in the near future) radio occultation payloads using not only signals from GPS but also from other GNSS systems, referred to as GNSS-RO payloads. Examples are the FORMOSAT/COSMIC constellation, the EUMETSAT-ESA's meteorological METOP series or the EU-ESA's Global Monitoring for Environmental Security Sentinel satellites.
However, the above missions require provision of a dedicated system aboard respective spacecraft for performing radio occultation, including dedicated antennas and dedicated signal processing circuitry as well as other electronic components. In view of increasingly tight constraints on the mass budget and volume budget for scientific payload in upcoming spaceborne missions, there is a need for an alternative radio occultation technique, and for a system performing such radio occultation technique. There is a further need for a radio occultation technique that may be performed using already existing infrastructure, and for a system performing such radio occultation technique.